An LTE network consists of an evolved universal terrestrial radio access network (E-UTRAN), evolved NodesB (eNBs) and an evolved packet core (EPC), wherein the to E-UTRAN comprises a set of eNBs connected with the EPC via interfaces S1, the eNBs are interconnected via interfaces X2, wherein the S1 and the X2 are logic interfaces. One EPC may manage one or more eNBs, and one eNB may be controlled by multiple EPCs and may manage one or more cells.
A self organizing network (SON) is a technology of automatic network configuration and optimization. This technology, characterized in self-configuration and self-optimization, is applied in an LTE network to make the LTE network configure network parameters automatically according to a given measurement and perform self-optimization according to network changes, thereby keeping the best network performance and saving plenty of human and material resources.
As for self-optimization of handover parameters of an LTE system, cell reselection and handover-related parameters are optimized according to a given algorithm based on the running status of the network and handover-related measurements so as to improve network performance. The handover herein means a handover within an LTE system and a handover between systems, the latter one is a handover to a UTRAN or a global system for mobile communication (GSM) or a code division multiple access (CDMA) system. A handover carried out by a user equipment (UE) in a network is that the network side makes a handover decision according to a given handover algorithm based on the signal quality of a cell covering the UE and a neighbouring cell reported by the UE, then notifies the UE to perform a concrete handover according to the handover decision. An inappropriate configuration of handover parameters may lead to an undesired Ping-Pong handover, which may cause a handover failure and a radio link failure (RLF), and may also have a negative effect on the user experience and waste network resources. Therefore, for self-optimization of handover parameters, an accurate judgment on a handover failure or an undesired handover is the foundation for the adjustments to handover parameters.
A radio resource control (RRC) may be re-established after an RLF happens to a UE, and user information may be stored in a source base station or a target base station for the RRC re-establishment. The UE may make a UE identifier contained in an RRC re-establishment request message, the UE identifier including a cell radio network temporary identifier (C-RNTI), a short medium access control integrity protection (short MAC-I) and a physical cell identity (PCI), wherein the C-RNTI is distributed in a source cell (a scene of a handover failure) or in a cell triggering an RRC re-establishment (other scenes). The PCI is the physical identity of a source cell (a scene of a handover failure) or the physical identity of a cell triggering an RRC re-establishment (other scenes).
The UE selects a cell for an RRC re-establishment mainly according to the quality of radio signals, so a judgment on a handover scene can be made based on a cell where an RLF happens and a cell where an RRC is re-established. An undesired handover scene herein means a too early handover or a handover selecting a wrong target handover cell; and handover parameters can be optimized according to statistical information about a specific undesired handover scene.
FIG. 1 is a schematic diagram of a scene of a too early handover; as illustrated in FIG. 1, shortly after a handover of a UE from Cell a of eNB A to Cell b of eNB B, an RLF happens in the Cell b, then the UE selects to perform an RRC re-establishment in the Cell a, that is, the UE returns to the original cell to perform an RRC re-establishment, this process shows that the handover of the UE from the Cell a to the Cell b is too early.
FIG. 2 is a schematic diagram of a scene of a handover selecting a wrong target handover cell; as illustrated in FIG. 2, shortly after a handover of a UE from Cell c of eNB C to Cell b of eNB B, an RLF happens, then the UE performs an RRC re-establishment in Cell a of eNB A, which means that the selected Cell b of the eNB B is a wrong target cell and the correct one is the Cell a, that is, the UE should directly perform a handover from the Cell c to the Cell a.
The judgment on a cell handover scene is the foundation for the configuration of handover parameters, if notified of a cell handover failure and the cause for the failure, the network side can configure handover parameters accordingly, thereby improving the success rate of a cell handover and avoiding a waste of network resources and a decline in the quality of communication service due to a wrong selection of a target handover cell.